Fiber-optic cables are becoming the standard means of communication signal transmission. Fiber optic cables can span the long distances between local phone systems as well as computer networks, cable television services, university campuses, office buildings, industrial plants, and electric utility companies. Fiber optics systems use light pulses to transmit information down fiber lines, or patchcords. A patchcord is a length of cable with a connector terminated at both ends. At one end of the system is a transmitter. The transmitter is the place of origin for information to be conveyed along the fiber lines. The transmitter utilizes a lens to funnel light pulses from a light emitting diode or a laser into the fiber optic medium, which in turn transmits the pulses down the line.
Connectors are used to mate a fiber to another fiber or to equipment. Connectors are used when one expects that the connection must occasionally be broken. A connector marks a place along a fiber optic line where signal power can be lost and the bit error rate can be affected. A good mechanical connection is required to ensure fiber optic reliability. Good coupling efficiency requires precise positioning of the connecting fibers. Optical connectors are similar to their electrical counterparts in function and outward appearance. They must, however, be high precision devices. A connector must center the fiber so that its light gathering core lies directly over and in line with a light source or another fiber to a tolerance of a few ten thousandths of an inch.
There are many different types of optical connectors in use today. The SC type connector has emerged as one of the most popular styles. The conventional SC connector is a push/pull connector that provides for accurate alignment via a ceramic ferrule on one patchcord (or piece of equipment) which mates with a ceramic alignment sleeve on another patchcord (or piece of equipment). A ferrule is a rigid portion of a fiber optic connector used to position and protect the fiber, allowing for repeated connection and disconnection. The conventional alignment sleeve 120, as depicted in FIGS. 1C and 1D, has a round opening of a diameter 121 just a few sub-microns greater than the diameter 111 of the ferrule 110, illustrated in FIGS. 1A and 1B. The alignment sleeve 120 is secured inside the optical connector receptacle 130 (FIGS. 1E and 1F). The ferrule 110 must fit into sleeve 120 tightly enough so that the fiber within ferrule 110 is properly aligned with the fiber or light source at the other end of the connector, yet loosely enough so that it may be removed and re-inserted repeatedly without damaging the fiber within.
It is imperative that the center of the circular opening in the alignment sleeve 120 is concentric with the center of the ferrule 110, where the actual fiber 115 is located. A misalignment of only a few sub-micron distances could result in decreased optical transmission power, if not complete transmission failure. The dimensions of ferrules and alignment sleeves are set forth by the Telecommunications Industry Association (TIA)/Electronic Industries Alliance (EIA) standards for fiber optic connector intermateability.
Proper optical alignment using the conventional method is achieved by maintaining extremely low machining tolerances during fabrication. Conventionally, the alignment sleeve is manufactured from expensive zirconia. Zirconia is hard enough to allow the required tight machining tolerances. The hardness of zirconia is also desirable because ferrules can be inserted and removed from a zirconia alignment sleeve repeatedly without damage to the sleeve. However, zirconia sleeves are costly, both due to the cost of zirconia itself and to the level of precision required during fabrication. As the number of applications of optical fiber communication continues to rise, reliable yet inexpensive alignment sleeves for connectors will become more and more desirable.